Recent years have seen increased interest in solar-powered unmanned aerial vehicles (UAVs), such as drones and balloons, for a variety of uses including surveillance, climate analysis, forest fire tracking, mapping, and telecommunications, among others. These advanced UAVs are equipped with solar panels and rechargeable batteries, allowing them to stay aloft and in service for potentially months or years at a time. Further, some such UAVs could be flown in the stratosphere, offering many of the advantages of traditional satellites but at a fraction of the cost.
By way of example, a representative “high altitude pseudo-satellite” or “HAPS platform” is a lightweight drone equipped with solar cells spread across its wings and with high-power lithium-sulphur batteries and propellers. Controlled from the ground or flying autonomously, the HAPS platform could climb to an altitude of around 70,000 feet (about 21 kilometers), which is above the weather and other air traffic but far below most satellites, and could carry mission payload such as high-resolution imaging and high-bandwidth communication equipment. During the day, the HAPS platform could use its solar panels to recharge its batteries. And at night, the platform could use the energy stored in its batteries to stay in flight.